Periodic ranging in a wireless access system for mobile station in sleep mode

ABSTRACT

A method of performing a ranging process between a base station and a mobile station in sleep mode in a wireless access system, wherein the base station provides the mobile station with an initial notification of a periodic ranging time that occurs during a sleep time interval and during which the mobile station is to perform the ranging process, the initial notification included in a first message, the first message indicating whether the mobile station should terminate sleep mode to receive downlink data, and wherein the base station provides the mobile station with subsequent notifications of periodic ranging times that occur during the sleep time interval, the subsequent notifications indicated in a second message, the second message transmitted to the mobile station as part of the ranging process such that the mobile station performs a plurality of ranging processes within the sleep time interval.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of application Ser. No. 11/674,991filed on Feb. 14, 2007 now U.S. Pat. No. 7,558,605, which is acontinuation of U.S. application Ser. No. 11/201,229, filed on Aug. 9,2005 now U.S. Pat. No. 7,194,288, and for which priority is claimedunder 35 U.S.C. §120; and this application claims priority ofapplication Ser. No. 10-2004-0062623, filed in Korea on Aug. 9, 2004,under 35 U.S.C. §119; the entire contents of all are hereby incorporatedby reference.

FIELD OF THE INVENTION

The present invention relates generally to a wireless access system and,more particularly, to a mobile station in sleep mode in a wirelessaccess system.

BACKGROUND OF THE INVENTION

A wireless access system supports a sleep mode of a mobile station inorder to minimize power consumption. A mobile station in a sleep mode isoperates according to a sleep interval, which increases at a certainratio. The sleep interval includes a listening window (e.g., listeninginterval) and a sleep window (e.g., sleep interval).

The listening interval is fixed by a sleep request message and a sleepresponse message, During the listening interval, a mobile stationreceives an indication of whether downlink traffic is being transmittedto the mobile station through a broadcast MAC management message (e.g.,MOB-TRF-IND) sent from a base station (BS). The mobile station alsoreceives an indication of whether ranging for maintaining uplinkcommunications and a proper downlink coding type based on signal qualityshould be performed.

The sleep interval is a period during which the mobile station receivesonly a minimum downlink signal from a base station in order to reducepower consumption. During the sleep interval, the mobile station scansneighboring base stations for a handover and performs ranging formaintaining uplink communications and a proper downlink coding typeaccording to signal quality.

The operation in the sleep mode includes transmitting and receiving aMAC management message, such as a sleep request (e.g., MOB-SLP-REQ)message, a sleep response (e.g., MOB-SLP-RSP) message or a broadcastdownlink traffic indication (e.g., MOB-TRF-IND) message, between amobile station and a base station.

FIG. 1 illustrates an exemplary sleep request message transmitted by amobile station to a serving base station to request sleep mode.

Referring to FIG. 1, the MOB-SLP-REQ message is a type of MAC managementmessage used for the sleep mode operation and includes a sleep intervaland a listening interval.

FIG. 2 illustrates an exemplary sleep response message transmitted bythe serving base station to the mobile station.

Referring to FIG. 2, the MOB-SLP-REQ message includes sleep mode-relatedinformation such as information regarding whether a sleep mode isapproved, a sleep interval, a listening interval, or a sleep ID.

FIG. 3 illustrates an exemplary broadcast traffic indication messagetransmitted to the mobile station at a certain interval.

Referring to FIG. 3, upon receiving the MOB-TRF-IND message during alistening interval, the mobile station in the sleep mode determineswhether to maintain the sleep mode, to terminate the sleep mode andreceive downlink data, or to perform ranging during a sleep interval.

FIG. 4 is a signal flow diagram illustrating operation in the sleepmode.

Referring to FIG. 4, a mobile station generates a sleep request (e.g.,MOB-SLP-REQ) message. The sleep request message includes values for aninitial sleep interval (e.g., initial sleep window), a final sleepinterval (e.g., final sleep window), and a listening interval. Themobile station then transmits the MOB-SLP-REQ message to a base stationto request transition to a sleep mode. The base station transmits to themobile station a sleep response (e.g., MOB-SLP-RSP) message in which theinitial sleep interval, the final sleep interval, the listeninginterval, and a conversion start frame are set, thereby approving thetransition to the sleep mode.

Accordingly, when a sleep mode conversion start time (e.g., M) has beenreached, the mobile station maintains a sleep mode during the initialsleep interval (e.g., N1 frame). Thereafter, when the initial sleepinterval expires, the mobile station receives a traffic indication(e.g., MOB-TRF-IND) message from the base station during a listeninginterval (e.g., L′). If no downlink traffic is being transmitted to themobile station (e.g., a negative indication), the mobile stationmaintains a sleep mode during a period that is twice (e.g., 2*N1) aslong as the initial sleep interval (e.g., N1).

The sleep interval is continuously increased according to theaforementioned equation such that the next sleep interval is set to betwice as long as the previous sleep interval. When the sleep intervalreaches the final sleep interval (e.g., N2), the mobile stationrepeatedly uses the final sleep interval as the next sleep interval. Thefinal sleep interval (e.g., sleep window) is set as follows according tothe parameters shown in FIG. 2.

Final sleep window=final sleep window*2^(final sleep window).

In contrast, if the mobile station is notified via a traffic indication(e.g., MOB-TRF-IND) message during the listening interval (e.g., apositive indication) that there is downlink traffic being transmitted tothe mobile station, the mobile station terminates the sleep mode andreceives the downlink traffic in a normal mode (e.g., awake mode).Furthermore, when receiving any uplink data, except for a rangingrequest (e.g., RNG-REQ) message, from the mobile station in sleep mode,the base station determines that the mobile station has terminated thesleep mode.

When there is no uplink signal from a specific mobile station during acertain period (e.g., a driving time of timer T27), the base stationallocates an uplink slot to the mobile station, thereby allowing themobile station to transmit to the base station a ranging request messagefor maintaining uplink synchronization (e.g., time, frequency and uplinktransmission power) and for maintaining a proper coding rate accordingto signal quality. The base station, having received the ranging requestmessage, sets a compensation value (e.g., time, frequency and uplinktransmission power) for maintaining the uplink synchronization in aranging response message and transmits the ranging response message tothe mobile station.

FIG. 5 illustrates periodic ranging of a mobile station in the sleepmode.

Referring to FIG. 5, the base station sets, in a broadcast trafficindication (e.g., MOB-TRF-IND) message, a ranging operation time (e.g.,ranging offset) and an information regarding whether or not the rangingis performed, and transmits the MOB-TRF-IND message to the mobilestation in a sleep mode. The mobile station in the sleep mode receivesthe MOB-TRF-IND message during a listening interval.

Thereafter, when the ranging time has been reached, the mobile stationtransmits a ranging request (e.g., RNG-REQ) message to the base stationusing the allocated uplink slot, and the base station transmits aranging response (e.g., RNG-RSP) message to the mobile station. The basestation allocates an uplink link bandwidth (e.g., UL BW) for a periodicRNG-REQ. Accordingly, the mobile station receives the ranging response(e.g., RNG-RSP) message, adjusts the uplink synchronization with thebase station, and maintains the sleep mode.

If there is a need for the mobile station in a sleep mode to performperiodic ranging during a sleep interval, the base station sets, in abroadcast MOB-TRF-IND message, a ranging operation time and informationregarding whether the ranging is performed, and transmits theMOB-TRF-IND message to the mobile station. Thereafter, when recognizingthat there is downlink traffic or that there is no ranging operationfrom the received MOB-TRF-IND message during the listening interval, themobile station maintains a sleep mode during a sleep interval that istwice as long as a present sleep interval.

FIG. 6 illustrates a relationship between a sleep ID (SLPID) bitmap anda sleep ID in a traffic indication message.

Referring to FIG. 6, the format of the MOB-TRF-IND message is the sameas that of FIG. 3.

For example, assuming that an SLPID bitmap of the MOB-TRF-IND is thesame as that shown in FIG. 6, SLPID mobile stations that should performperiodic ranging are indicated. Assuming a number of mobile stationsperforming periodic ranging is seven, a ranging time (e.g., rangingframe offset) of each mobile station is set as follows.

Ranging frame offset 1: frame offset of SLPID 2

Ranging frame offset 2: frame offset of SLPID 8

Ranging frame offset 3: frame offset of SLPID 9

Ranging frame offset 4: frame offset of SLPID 12

Ranging frame offset 5: frame offset of SLPID 15

Ranging frame offset 6: frame offset of SLPID 18

Ranging frame offset 7: frame offset of SLPID 20

Therefore, a single mobile station may perform only one periodic rangingduring the next sleep interval after a listening interval. Only oneperiodic ranging may be performed by the single mobile station because,while the SLPID bitmap may indicate whether or not the ranging isperformed, the SLPID bitmap may not indicate the number of times thatranging is to be performed.

In the related art, the base station performs periodic ranging using aspecific timer (e.g., T27). If the base station cannot receive anyuplink signal from a specific mobile station before the timer expires,the base station allocates an uplink slot to a mobile station to allowthe mobile station to transmit a ranging request message to the basestation and to perform the ranging operation. If the base stationreceives the uplink signal from the specific mobile station before thecorresponding timer expires, the timer is reset. As described above, thesleep interval of a sleep mode increases exponentially from an initialsleep interval to a final sleep interval. The final sleep interval(e.g., sleep window) is set through a predetermined formula.

FIG. 7 illustrates a relationship between a periodic ranging period anda sleep interval.

Referring to FIG. 7, if a sleep interval is longer than a periodicranging cycle, the mobile station is requested to perform periodicranging two or more times during a corresponding sleep interval.However, in the related art, periodic ranging with respect to a singlemobile station may not be performed more than once during a sleepinterval, which creates problems because periodic ranging during thesleep mode may not be provided.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to periodic ranging in awireless access system that substantially obviates one or more problemsdue to limitations and disadvantages of the related art.

An object of the present invention is to perform a plurality of periodicranging operations during a single sleep interval.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein, inone embodiment, a method of performing a ranging process between a basestation and a mobile station in sleep mode in a wireless access systemcomprises, wherein the base station provides the mobile station with aninitial notification of a periodic ranging time that occurs during asleep time interval and during which the mobile station is to performthe ranging process, the initial notification included in a firstmessage, the first message indicating whether the mobile station shouldterminate sleep mode to receive downlink data, and provides the mobilestation with subsequent notifications of periodic ranging times thatoccur during the sleep time interval, the subsequent notificationsindicated in a second message, the second message transmitted to themobile station as part of the ranging process such that the mobilestation performs a plurality of ranging processes within the sleep timeinterval.

The first message may be a traffic indicator message and the secondmessage may be a ranging response message. The subsequent notificationsof periodic ranging times in the second message may comprise a typelength value (TLV) form. The initial notification of periodic rangingtime in the first message may comprise a type length value (TLV) form.The second message may comprise an indication whether the mobile stationshould terminate sleep mode to receive downlink data. The indicationwhether the mobile station should terminate sleep mode to receivedownlink data may comprise a type length value (TLV) form.

In another embodiment, a method of performing a ranging process betweena base station and a mobile station in sleep mode in a wireless accesssystem comprises, in the mobile station, setting a sleep time intervalduring which the mobile station remains in sleep mode. The method alsocomprises, in the base station, transmitting a first message to themobile station at a predetermined listening time, the first messageindicating whether the mobile station should terminate sleep mode toreceive downlink data and indicating an initial periodic ranging timeduring which the mobile station is to perform the ranging process. Themethod also comprises, in the mobile station, performing the rangingprocess at the indicated initial periodic ranging time. The method alsocomprises, in the base station, transmitting a second message to themobile station in response to the mobile station performing the rangingprocess, the second message comprising information required forperforming the ranging process and, if a subsequent periodic rangingtime is determined to occur during the sleep time interval, furtherindicating the subsequent periodic ranging time.

In yet another embodiment, a method of performing a ranging processbetween a base station and a mobile station in sleep mode in a wirelessaccess system comprises transmitting a first message to the mobilestation at a predetermined listening time during a sleep time interval,the first message indicating whether the mobile station should terminatesleep mode to receive downlink data and indicating an initial periodicranging time during which the mobile station is to perform the rangingprocess. The method also comprises determining, in response to themobile station performing the ranging process, whether a subsequentperiodic ranging time occurs during the sleep time interval. The methodalso comprises transmitting a second message to the mobile station, thesecond message comprising information required for performing theranging process and, if the subsequent periodic ranging time wasdetermined to occur during the sleep time interval, further indicatingthe subsequent periodic ranging time.

In still another embodiment, a method of performing a ranging processbetween a base station and a mobile station in sleep mode in a wirelessaccess system comprises setting and remaining in sleep mode during asleep time interval. The method also comprises receiving a first messageat a predetermined listening time, the first message indicating whethersleep mode should be terminated to receive downlink data and indicatingan initial periodic ranging time. The method also comprises performingthe ranging process at the indicated initial periodic ranging time. Themethod also comprises receiving a second message, the second messagecomprising information required for performing the ranging process andindicating a subsequent periodic ranging time. The method also comprisesperforming the ranging process at the subsequent periodic ranging time.

In yet another embodiment, a method of performing a ranging processbetween a base station and a mobile station in a wireless access system,wherein the base station provides the mobile station with an initialnotification of a periodic ranging time that occurs during a sleep timeinterval and during which the mobile station is to perform the rangingprocess, the initial notification included in a first message, the firstmessage indicating whether the mobile station should enter sleep mode,and wherein the base station provides the mobile station with subsequentnotifications of periodic ranging times that occur during the sleep timeinterval, the subsequent notifications indicated in a second message,the second message transmitted to the mobile station as part of theranging process such that the mobile station performs a plurality ofranging processes within the sleep time interval.

The foregoing and other objects, features, aspects and advantages of thepresent invention will become more apparent from the following detaileddescription of the present invention when taken in conjunction with theaccompanying drawings. It is to be understood that both the foregoinggeneral description and the following detailed description of thepresent invention are exemplary and explanatory and are intended toprovide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 illustrates an exemplary sleep request message transmitted by amobile station to a serving base station to request sleep mode.

FIG. 2 illustrates an exemplary sleep response message transmitted bythe serving base station to the mobile station.

FIG. 3 illustrates an exemplary broadcast traffic indication messagetransmitted to the mobile station at a certain interval.

FIG. 4 is a signal flow diagram illustrating conventional operation inthe sleep mode.

FIG. 5 illustrates periodic ranging of a mobile station in the sleepmode.

FIG. 6 illustrates a relationship between a sleep ID bitmap and a sleepID in a traffic indication message.

FIG. 7 illustrates a relationship between a periodic ranging period anda sleep interval.

FIG. 8 illustrates an exemplary transmission of the next ranging time ina ranging response message, according to an embodiment of the presentinvention.

FIG. 9 illustrates an exemplary notification of the mobile station of aperiodic ranging cycle and an initial ranging time through a sleepresponse message, according to an embodiment of the present invention.

FIG. 10 illustrates a periodic ranging method for a mobile station insleep mode, according to an embodiment of the present invention.

FIG. 11 illustrates a periodic ranging method for a mobile station insleep mode, according to another embodiment of the present invention.

FIG. 12 illustrates a periodic ranging method for a mobile station insleep mode, according to yet another embodiment of the presentinvention.

FIG. 13 illustrates an exemplary notification to the mobile station ofgeneration of downlink traffic being transmitted to the mobile stationin the sleep mode during a sleep interval in a periodic ranging processthrough a periodic ranging response message, according to an embodimentof the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

The present invention may enable a mobile station (MS) in a sleep modeto perform periodic ranging more than once during a single sleepinterval, when the sleep interval is longer than a ranging cycle.Accordingly, various ranging methods are discussed.

In a first ranging method, a base station notifies a mobile station of anext ranging time (e.g., ranging offset) through a ranging response(e.g., RNG-RSP) message. In a second ranging method, a base stationnotifies a mobile station of a periodic ranging time that is initiallyperformed after transitioning into a sleep mode through a sleep response(e.g., MOB-SLP-RSP) message, and notifies the mobile station of a nextperiodic ranging time through a ranging response (e.g., RNG-RSP)message. In a third ranging method, a base station notifies a mobilestation of an initial periodic ranging time and a next ranging cyclethrough a sleep response (e.g., MOB-SLP-RSP) message to the mobilestation upon transition to a sleep mode.

The first ranging method may be used for mobile stations that mustperform a plurality of periodic ranging operations during a single sleepinterval. The mobile station is notified of a time of the initialperiodic ranging during a sleep interval through a traffic indication(e.g., MOB-TRF-IND) message and is notified of a time of the nextperiodic ranging through a ranging response (e.g., RNG-RSP) message.

The second ranging method may enable a mobile station in sleep mode toperform periodic ranging regardless of a sleep interval. Unlike thefirst ranging method, the mobile station is notified of the time of theinitial periodic ranging after transition to a sleep mode through asleep response (e.g., MOB-SLP-RSP), not through a MOB-TRF-IND message.

In the third ranging method, the mobile station is notified of a rangingperiod through a sleep response (e.g., MOB-SLP-RSP) message. Thus, thethird ranging method may be distinguished from the first and secondranging methods in that the mobile station is notified of the rangingperiod through a sleep response message, and not a periodic rangingresponse (e.g., RNG-RSP) message, When the second and third rangingmethods are used, a broadcast traffic indication message MOB-TRF-INDrequired for a sleep mode operation may exclude a part related to aperiodic ranging function.

FIG. 8 illustrates an exemplary transmission of the next ranging time ina ranging response message, according to an embodiment of the presentinvention. FIG. 9 illustrates an exemplary notification of the mobilestation of a periodic ranging cycle and an initial ranging time througha sleep response message, according to an embodiment of the presentinvention. In the first and second ranging methods, the next periodicranging time may be included in a ranging response (e.g., RNG-RSP)message in a TLV form (Type Length Value) illustrated in FIG. 8. In thethird ranging method, the initial periodic ranging time and the nextranging cycle may be included in a sleep response (e.g., MOB-SLP-RSP),illustrated in FIG. 9. Furthermore, the second ranging method may usethe sleep response message of FIG. 9 that excludes a periodic rangingcycle.

A periodic ranging method of a mobile station in sleep mode inaccordance with preferred embodiments of the present invention will nowbe described in more detail.

FIG. 10 illustrates a periodic ranging method for a mobile station insleep mode, according to an embodiment of the present invention. Inparticular, FIG. 10 shows an example of the first ranging method inwhich the mobile station in sleep mode may perform a plurality ofperiodic ranging operations during a single sleep interval.

Referring to FIG. 10, a mobile station receives a traffic indication(e.g., MOB-TRF-IND) message sent from a base station during a listeninginterval. The base station notifies a mobile station that must performperiodic ranging during a sleep interval of a time (e.g., point) ofranging by a ranging frame offset through the MOB-TRF-IND message. Whena ranging start time (e.g., ranging frame offset) has been reached whilethe mobile station maintains the sleep mode, the mobile stationtransmits to the base station a ranging request (e.g., RNG-REQ) messagethrough an uplink slot allocated by the base station.

The base station checks whether a next periodic ranging time of themobile station that transmitted the RNG-REQ message is within a currentsleep interval. If the next periodic ranging time is within the currentsleep interval, the base station includes the next ranging time in aranging response (e.g., RNG-RSP) message and transmits the RNG-RSPmessage to the mobile station. The mobile station, upon receiving thenext ranging time through the ranging response (e.g., RNG-RSP) message,maintains the sleep mode. When the next ranging time is reached, themobile station transmits to the base station the RNG-REQ message throughan uplink slot allocated by the base station.

The base station checks whether the next periodic ranging time of themobile station that transmitted the RNG-REQ message is within a currentsleep interval. If the next periodic ranging time is not within thecurrent sleep interval, the base station does not include the nextranging time in the ranging response message but instead transmits theRNG-RSP message to the mobile station.

Accordingly, upon receiving the RNG-RSP message which does not includethe next ranging point, the mobile station maintains the sleep modeduring a sleep interval. When a listening interval is reached, themobile station receives a traffic indication (e.g., MOB-TRF-IND) messagefrom the base station including information regarding whether there isdownlink traffic being transmitted to the mobile station or there is aneed to perform ranging during the sleep interval.

Upon receiving a ranging request (e.g., RNG-REQ) message, a downlinkburst profile change request (e.g., DBPC-REQ) or other uplink messageaside from periodic ranging from the mobile station during a sleepinterval, the base station updates a periodic ranging timer (e.g., T27).If a next periodic ranging time is within the corresponding sleepinterval, the base station includes the next periodic ranging time inthe RNG-RSP message or the DBPC-RSP message and transmits the message tothe mobile station.

FIG. 11 illustrates a periodic ranging method for a mobile station insleep mode, according to another embodiment of the present invention. Inparticular, FIG. 11 shows an example of the second ranging method inwhich the mobile station in sleep mode may perform a plurality ofperiodic ranging operations during a single sleep interval.

Referring to FIG. 11, the mobile station transmits a sleep request(e.g., MOB-SLP-REQ) message to a base station to request transition to asleep mode. The base station includes in a sleep response (e.g.,MOB-SLP-RSP) message, an initial periodic ranging time after thetransition to the sleep mode, and transmits the message to the mobilestation.

The mobile station gradually increases a sleep interval according to analgorithm and receives a traffic indication (e.g., MOB-TRF-IND) messageduring a listening interval in order to check whether downlink trafficis being transmitted to the mobile station. When the initial periodicranging time has been reached, the mobile station transmits to the basestation a ranging request (e.g., RNG-REQ) message through an uplink slotallocated by the base station.

The base station, upon receiving the RNG-REQ message, includes a pointof the next periodic ranging in a ranging response (e.g., RNG-RSP)message and transmits the message to the mobile station. The mobilestation having received the next periodic ranging time through theRNG-RSP message transmits a ranging request (e.g., RNG-REQ) messagethrough an uplink slot allocated from the base station when thecorresponding time has been reached.

Upon receiving a ranging request (e.g., RNG-REQ) message, a downlinkburst profile change request (e.g., DBPC-REQ) message or other uplinkmessage aside from periodic ranging from the mobile station in sleepmode, the base station updates a periodic ranging timer, includes a nextperiodic ranging time in a ranging response message or a downlink burstprofile change response (e.g., DBPC-RSP) message, and transmits themessage to the mobile station.

In the second ranging method, information regarding whether the rangingis performed is not transmitted through a traffic indication (e.g.,MOB-TRF-IND) message. Instead, a mobile station in sleep mode receivesthe next periodic ranging time through the ranging response message,regardless of a sleep interval.

FIG. 12 illustrates a periodic ranging method for a mobile station insleep mode, according to yet another embodiment of the presentinvention. In particular, FIG. 12 shows an example of the third rangingmethod in which the mobile station in sleep mode may perform a pluralityof periodic ranging operations during a single sleep interval.

Referring to FIG. 12, the mobile station transmits a sleep request(e.g., MOB-SLP-REQ) message to a base station to request transition to asleep mode. The base station, in response, may prepare and transmit asleep response (e.g., MOB-SLP-RSP) message that includes an initialperiodic ranging time after the transition to the sleep mode, and aperiodic ranging cycle.

The mobile station gradually increases a sleep interval according to analgorithm, receives a traffic indication (e.g., MOB-TRF-IND) messageduring a listening interval, and checks whether there is downlinktraffic being transmitted to the mobile station. When the initialperiodic ranging time has been reached, the mobile station transmits aranging request (e.g., RNG-REQ) message through an uplink slot allocatedfrom the base station.

The base station, upon receiving the ranging request (e.g., RNG-REQ)message, transmits a ranging response (e.g., RNG-RSP) message to themobile station. When the periodic ranging cycle included in the sleepresponse (e.g., MOB-SLP-RSP) message has been reached, the mobilestation transmits a ranging request (e.g., RNG-REQ) message through anuplink slot allocated from the base station. The base station, uponreceiving the ranging request (e.g., RNG-REQ) message, transmits aranging response (e.g., RNG-RSP) message to the mobile station. Then,while maintaining a sleep mode, the mobile station repetitivelytransmits and receives the ranging request (e.g., RNG-REQ) message andthe ranging response (e.g., RNG-RSP) message.

FIG. 13 illustrates an exemplary notification to the mobile station ofgeneration of downlink traffic being transmitted to the mobile stationin the sleep mode during a sleep interval in a periodic ranging processthrough a periodic ranging response message, according to an embodimentof the present invention.

In a conventional approach, when downlink traffic is generated during asleep interval, the mobile station is notified of the generation of thedownlink traffic through a traffic indication (e.g., MOB-TRF-IND)message transmitted during a listening interval after a correspondingsleep interval expires. However, if the sleep interval is too long,problems may occur in that the base station must perform buffering ofdownlink data for a long time to avoid data loss.

Therefore, in a fourth ranging method, when a mobile station performsperiodic ranging during the sleep interval, the base station notifiesthe mobile station of the downlink traffic generation through a rangingresponse (e.g., RNG-RSP) message, such that the mobile stationterminates a sleep mode during the sleep interval and receives data. Asan example of a ranging response message setting, a value of rangingoffset TLV may be set as 0 to indicate downlink traffic generation.

In one embodiment, a method of performing a ranging process between abase station and a mobile station in sleep mode in a wireless accesssystem, wherein the base station provides the mobile station with aninitial notification of a periodic ranging time that occurs during asleep time interval and during which the mobile station is to performthe ranging process, the initial notification included in a firstmessage, the first message indicating whether the mobile station shouldterminate sleep mode to receive downlink data, and wherein the basestation provides the mobile station with subsequent notifications ofperiodic ranging times that occur during the sleep time interval, thesubsequent notifications indicated in a second message, the secondmessage transmitted to the mobile station as part of the ranging processsuch that the mobile station performs a plurality of ranging processeswithin the sleep time interval.

The first message may be a traffic indicator message and the secondmessage may be a ranging response message. The subsequent notificationsof periodic ranging times in the second message may comprise a typelength value (TLV) form. The initial notification of periodic rangingtime in the first message may comprise a type length value (TLV) form.The second message may comprise an indication whether the mobile stationshould terminate sleep mode to receive downlink data. The indicationwhether the mobile station should terminate sleep mode to receivedownlink data may comprise a type length value (TLV) form.

In another embodiment, a method of performing a ranging process betweena base station and a mobile station in sleep mode in a wireless accesssystem comprises, in the mobile station, setting a sleep time intervalduring which the mobile station remains in sleep mode. The method alsocomprises, in the base station, transmitting a first message to themobile station at a predetermined listening time, the first messageindicating whether the mobile station should terminate sleep mode toreceive downlink data and indicating an initial periodic ranging timeduring which the mobile station is to perform the ranging process. Themethod also comprises, in the mobile station, performing the rangingprocess at the indicated initial periodic ranging time. The method alsocomprises, in the base station, transmitting a second message to themobile station in response to the mobile station performing the rangingprocess, the second message comprising information required forperforming the ranging process and, if a subsequent periodic rangingtime is determined to occur during the sleep time interval, furtherindicating the subsequent periodic ranging time.

In yet another embodiment, a method of performing a ranging processbetween a base station and a mobile station in sleep mode in a wirelessaccess system comprises transmitting a first message to the mobilestation at a predetermined listening time during a sleep time interval,the first message indicating whether the mobile station should terminatesleep mode to receive downlink data and indicating an initial periodicranging time during which the mobile station is to perform the rangingprocess. The method also comprises determining, in response to themobile station performing the ranging process, whether a subsequentperiodic ranging time occurs during the sleep time interval. The methodalso comprises transmitting a second message to the mobile station, thesecond message comprising information required for performing theranging process and, if the subsequent periodic ranging time wasdetermined to occur during the sleep time interval, further indicatingthe subsequent periodic ranging time.

In still another embodiment, a method of performing a ranging processbetween a base station and a mobile station in sleep mode in a wirelessaccess system comprises setting and remaining in sleep mode during asleep time interval. The method also comprises receiving a first messageat a predetermined listening time, the first message indicating whethersleep mode should be terminated to receive downlink data and indicatingan initial periodic ranging time. The method also comprises performingthe ranging process at the indicated initial periodic ranging time. Themethod also comprises receiving a second message, the second messagecomprising information required for performing the ranging process andindicating a subsequent periodic ranging time. The method also comprisesperforming the ranging process at the subsequent periodic ranging time.

In yet another embodiment, a method of performing a ranging processbetween a base station and a mobile station in a wireless access system,wherein the base station provides the mobile station with an initialnotification of a periodic ranging time that occurs during a sleep timeinterval and during which the mobile station is to perform the rangingprocess, the initial notification included in a first message, the firstmessage indicating whether the mobile station should enter sleep mode,and wherein the base station provides the mobile station with subsequentnotifications of periodic ranging times that occur during the sleep timeinterval, the subsequent notifications indicated in a second message,the second message transmitted to the mobile station as part of theranging process such that the mobile station performs a plurality ofranging processes within the sleep time interval.

Furthermore, the ranging method for a mobile station in sleep mode inaccordance with preferred embodiments of the present invention may beused not only for the periodic ranging but also as a method in which abase station examines effectiveness of the mobile station. Specifically,the method may be applied for updating effectiveness with respect to themobile station as the base station enables the mobile station to performranging and receives a ranging request message from the mobile station.

The present invention may enable a mobile station in a sleep mode toperform periodic ranging regardless of a sleep interval. Particularly,one ranging method is advantageous in that the mobile station in sleepmode may perform periodic ranging while maintaining the sleep modeoperation in accordance with the related art. Another ranging method isadvantageous in that a length of a traffic indication message sent tothe mobile station in sleep mode may be reduced and radio resourcesrequired for traffic indication message transmission may also be reducedby excluding a part related to a periodic ranging function from abroadcast traffic indication message required for a sleep modeoperation.

It will be apparent to those skilled in the art that variousmodifications and variations may be made in the present inventionwithout departing from the spirit or scope of the inventions. Thus, itis intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

What is claimed is:
 1. A method of performing a ranging process betweena base station and a mobile station in a wireless access system,comprising: transmitting a sleep request message to a base station torequest transition to a sleep mode; receiving a sleep response messagein response to the sleep request message from the base station, whereinthe sleep response message comprises a periodic ranging time; enteringthe sleep mode; transmitting a ranging request through uplink resourcesallocated by the base station when the periodic ranging time is reached;receiving a ranging response message from the base station in responseto the ranging request message, wherein the ranging response messagecomprises a next periodic ranging time; if a value of the next periodicranging time in the ranging response message is set to zero to indicatean existence of downlink data, terminating the sleep mode; and if avalue of the next periodic ranging time is not zero, transmittinganother ranging request message through the resources allocated by thebase station when the next periodic ranging time has been reached. 2.The method of claim 1, further comprising: receiving a trafficindication message during a listen interval, wherein the trafficindication message indicates whether or not the mobile station shouldterminate the sleep mode to receive downlink data.
 3. The method ofclaim 1, wherein the periodic ranging time in the sleep response messageand the next periodic ranging time in the ranging response message eachhave a type length value (TLV) form.
 4. A mobile subscriber station of awireless communication system, the mobile subscriber station comprising:a radio frequency (RF) unit configured to: transmit a sleep requestmessage to a base station to request transition to a sleep mode; receivea sleep response message in response to the sleep request message fromthe base station, wherein the sleep response message comprises aperiodic ranging time; enter the sleep mode; transmit a ranging requestthrough uplink resources allocated by the base station when the periodicranging time is reached; receive a ranging response message from thebase station in response to the ranging request message, wherein theranging response message comprises a next periodic ranging time; if avalue of the next periodic ranging time in the ranging response messageis set to zero to indicate an existence of downlink data, terminate thesleep mode; and if a value of the next periodic ranging time is notzero, transmitting another ranging request message through the resourcesallocated by the base station when the next periodic ranging time hasbeen reached.
 5. The mobile subscriber station of claim 4, wherein theRF unit is further configured to: receive a traffic indication messageduring a listen interval, wherein the traffic indication messageindicates whether or not the mobile station should terminate the sleepmode to receive downlink data.
 6. The mobile subscriber station of claim4, wherein the periodic ranging time in the sleep response message andthe next periodic ranging time in the ranging response message each havea type length value (TLV) form.